The candidate?s long-term goal is to develop exercise prescriptions that improve physical and psychosocial health of survivors of sudden cardiac arrest (SCA). To achieve this goal a focused research career development Plan is proposed, including intensive study of: 1) cardiopulmonary exercise and metabolic testing, 2) measurement of cardiac autonomic nervous system function (heart rate variability), and 3) advanced statistical analysis of heart rate data. The purpose of this proposal is to determine the safety and feasibility of an exercise intervention in survivors (N= 10) of SCA who have automatic internal cardioverter defibrillators (ICDs). Secondarily, testing the impact of exercise on cardiac autonomic function (heart rate variability (HRV), health outcomes (heart rhythm stability, general health related quality of life, psychological distress), and major adverse cardiac events (cardiac hospitalizations, ER visits, and cardiac mortality) is proposed. The primary outcomes are safety and feasibility in implementing the exercise intervention from baseline to 8 weeks. SCA claims approximately 300,000 lives in the US per year, representing 40 percent of the total deaths resulting from cardiovascular disease. SCA often occurs outside the hospital without warning, where most resuscitated victims receive an ICD at the time of hospitalization. Approximately 29 percent of persons survive the initial cardiac arrest, with greater than 40,000 persons/year undergoing ICD implantation. The development of malignant ventricular arrhythmias at the time of SCA has been attributed in part to imbalances in autonomic nervous system function. Increased sympathetic nervous system activity and decreased parasympathetic activity has been shown to result in more ventricular arrhythmias. Protection against SCA may be achieved through mechanisms that increase parasympathetic tone, exercise being one of these therapies. Exercise training is an inexpensive, nonpharmacological intervention that is essentially devoid of negative side effects and virtually available to everyone. My interest is in determining if exercise will affect cardiac parasympathetic nervous system regulation and therefore convey cardioprotective effects that will subsequently influence rates of recurrence of ventricular arrhythmias, ICD shocks, and cardiac mortality. The results of this study have the potential to impact future exercise recommendations and prescriptions, feasibility, safety, and quality of life in SCA survivors with ICD?s.